<template>
  <div class="pagination">
    <h1>{{ startNumAndEndNum }}-------当前页码{{ pageNo }}</h1>
    <button :disabled="pageNo == 1" @click="$emit('getPageNo', pageNo - 1)">
      上一页
    </button>
    <button v-if="startNumAndEndNum.start > 1"
       @click="$emit('getPageNo', 1)"
       :class="{active: pageNo == 1}"
       >
      1
    </button>
    <button v-if="startNumAndEndNum.start > 2">···</button>

    <!-- 中间部分 page是点击的当前页码-->
    <button
      v-for="(page, index) in startNumAndEndNum.end"
      :key="index"
      v-show="page >= startNumAndEndNum.start"
      @click="$emit('getPageNo', page)"
      :class="{active: pageNo == page}"
    >
      {{ page }}
    </button>

    <!-- 下   -->
    <button v-if="startNumAndEndNum.end < totalPage - 1">···</button>
    <button
      v-if="startNumAndEndNum.end < totalPage"
      @click="$emit('getPageNo', totalPage)"
    >
      {{ totalPage }}
    </button>
    <button
      :disabled="pageNo == totalPage"
      @click="$emit('getPageNo', pageNo + 1)"
    >
      下一页
    </button>
    <!-- <h1>totalPage {{ totalPage - 1 }}</h1> -->
    <button style="margin-left: 30px">共 {{ total }} 条</button>
  </div>
</template>
  <script>
export default {
  name: "Pagination",
  //pageSize最大页数   continues连续数  pageNo 当前页  total 总数
  props: ["pageNo", "pageSize", "total", "continues"],
  computed: {
    //总共多少页
    totalPage() {
      //向上取整
      return Math.ceil(this.total / this.pageSize);
    },
    //计算出连续的页码的起始数字与结束数字【连续页码数字：至少是5】
    startNumAndEndNum() {
      const { continues, pageNo, totalPage } = this;

      //先定义两个变量存储其实是数字与结束数字
      let start = 0,
        end = 0;
      //连续页码数字5【就是至少5页】，如果出现不正常现象 不足5页
      //不正常现象【总页数没有连续页码多】
      if (continues > totalPage) {
        start = 1;
        end = totalPage;
      } else {
        //正常现象【连续页码5 ，但是你的总页数一定大于5的】
        //起始数字
        start = pageNo - parseInt(continues / 2);
        //结束数字
        end = pageNo + parseInt(continues / 2);
        //把出现不正常的现象 【start数字出现0 | 负数】纠正
        if (start < 1) {
          start = 1;
          end = continues;
        }
        //把出现不正常的现象[end数字大于总页码] 纠正
        if (end > totalPage) {
          end = totalPage;
          start = totalPage - continues + 1;
        }
      }
      return { start, end };
    },
  },
};
</script>
  
  <style lang="less" scoped>
.pagination {
  text-align: center;
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
</style>
  